1. Field of the Invention
The present invention relates to an alternator for use in an automotive vehicle, the alternator including a cooling fan.
2. Description of Related Art
An alternator is usually mounted on an automotive vehicle. Alternating current generated in the alternator according to rotation of a rotor is rectified into a direct current, and the on-board battery is charged with the rectified direct current. Cooling fans are mounted on axial ends of the rotor for cooling stator coils. Outside air is sucked into the alternator through inlet ports formed on an axial end wall of a housing according to rotation of the cooling fan, and the cooling air is exhausted from outlet ports formed on a radial outer wall of the housing. In other words, the outside air introduced in the axial direction cools the stator coil and is exhausted in the radial direction of the housing.
Airflow noise is generated in the vicinity of the outlet ports because the cooling airflow is disturbed there. The cooling airflow is also disturbed in the vicinity of the inlet ports where ribs and spokes of the housing are formed. Therefore, airflow noise is also generated in the vicinity of the inlet ports.
Various proposals have been made hitherto to reduce the airflow noise in the vicinity of the outlet ports. Such proposals include: changing a shape of blades of the cooling fan; improving a form of a coil end of the stator coil; and changing a shape of the outlet ports. By utilizing one or more of these proposals, it has been possible to suppress disturbance of the airflow in the vicinity of the outlet ports and to reduce the airflow noise around the outlet ports.
On the other hand, to reduce the airflow noise generated around the inlet ports, WO-00/16467 proposes to tilt housing ribs in the direction opposite to the rotational direction of the rotor with respect to the radial direction. It proposes to set the tilt angle in a range from 25 to 35 degrees. However, it has been found out that the airflow noise is not sufficiently reduced by tilting the ribs. This is because the size of the ribs formed on the axial end wall of the housing is not large enough both in the axial direction and along the rotational direction of the rotor. The ribs are formed only for preventing foreign particles such as small stones or the like from entering into the housing through the inlet ports. Therefore, the ribs are made much smaller in size than spokes for connecting a bearing box to a cylindrical portion of the housing.